End-point detection of the potentiometric titration of anionic polyelectrolytes using an anionic surfactant-selective plasticized poly (vinyl chloride) membrane electrode and an anionic surfactant as a marker ion

A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to d odecylbenzenesulfonate (DBS) ion is applied to the determination of anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) by potentio metric titration, using a poly (diallyldimethylammonium chloride) (Cat-floc ) solution as a titrant. The end-point of the titration is detected as the potential jump of the plasticized PVC membrane electrode caused by decrease in the concentration of DBS ion added to the sample solution as a marker i on, due to the ion association reaction between the DBS ion and Cat-floc. T he effects of the concentration of DBS ion, coexisting surfactants and elec trolytes in the sample solution and pH of the sample on the degree of the p otential jump at the end-point were examined. A linear relationship between the concentration of anionic polyelectrolyte and the end-point volume of t he titrant exists in the concentration range from 2 x 10(-5) to 4 x 10(-4) N for PVSK, alginate, and carrageenan.